Electrochemical cells, such as those containing lithium metal or alloy as an electrochemically active material, are utilized to provide power to various electronic devices. Electronic device manufacturers often design their devices to accept electrochemical cells having various standardized container exterior dimensions, such as “AA” or “AAA” sizes, or according to ANSI nomenclature, R6 or R03 size containers, respectively. Regulatory bodies such as the United Nations (UN) and Department of Transportation (DOT) have mandated requirements regarding transportation of lithium-containing electrochemical cells. In addition to regulating the maximum lithium content for a certain cell type, UN/DOT regulations require that lithium-containing cells pass mass loss tests, for example a T1 altitude simulation test and a T2 thermal cycling test.
Mass or weight loss in electrochemical cells can be attributed to sources such as diffusion of electrolyte vapor through a sealing member of the cell and electrolyte leakage at sealing interfaces, especially during temperature cycling. The diffusion weight loss can be calculated in one embodiment as a product of the vapor transmission rate of the sealing member, the dimensional ratio of the sealing member, and time. The dimensional ratio can be calculated by dividing the cross section area through which the electrolyte vapor diffuses with the path length that the vapor travels. As cell size decreases, the ratio of the cross section area to the path length does not decrease as quickly as the volume or the mass of the cell. Therefore, relatively small size cells tend to have higher percentage mass loss than larger cells, and it is believed to be more difficult for small size cells to pass UN/DOT mass loss requirements.
Moreover, electrochemical cells such as electrochemically active lithium-containing cells often utilize a non-aqueous electrolyte solution and salt that can be volatile and/or reactive. In view thereof, it is a challenge to construct an electrochemical cell that minimizes mass loss due to vapor transmission.
A further challenge is to provide the cell with a pressure release vent member for releasing or discharging fluid from inside the cell to limit the build-up of internal pressure while maintaining a seal during normal discharge or storage conditions. Without a vent member, the cell may fail, bulge, leak and/or disassemble.
Various pressure release vent member and closure assembly configurations have been used in electrochemical cells.
U.S. Pat. No. 3,279,953 relates to reportedly insulating seals for the metallic casing of sealed battery cells. Specifically, it relates to the insulating seal junction between the open end of the tubular metallic sheet casing and the metallic sheet cover enclosure which also constitutes the two opposite-polarity terminals of sealed cells, such as reportedly used, for example, in flashlights, although similar sealed casings have also been used in other applications.
U.S. Pat. No. 3,852,117 relates to a seal for an electrochemical cell or the like located between the cylinder wall and closure disc at one end of a cylindrical container. The seal comprises opposed circular sealing members formed by deformation of the cylinder wall, bearing against opposite faces of the disc around its rim. The seal is closed by axial compression of the cylinder wall causing deformation of the wall to form the sealing members and to press such members against the closure disc.
U.S. Pat. No. 5,876,868 relates to a battery sealing structure with a reportedly explosion-proof function of preventing battery explosion due to an abnormal increase of the inner pressure in the battery and also which reportedly is capable of excellently sealing the battery which may contribute to improvements in battery assembly operation efficiency.
U.S. Pat. No. 6,207,320 relates to a battery including a can filled with an electrolyte and an electrode assembly. A cap assembly is reportedly close-tightly mounted on an upper end of the can with a gasket interposed between the cap assembly and the upper end. The cap assembly provides a plate provided with a safety groove, a current control member disposed on the plate, a cap cover disposed on the current control member, and a circuit breaker disposed under the plate and supported by a support plate. Also, the circumferential edge of at least one of the plate, the current control member and the cap cover is bent around the support plate.
U.S. Pat. No. 6,620,544 relates to a sealed battery which includes a can for receiving an electric generator, a sealing member crimped on an opening of the can and connected to one of a positive electrode and a negative electrode of the electric generator, a gasket disposed between the can and the sealing member, a cover cap disposed on the sealing member with an insulating member disposed between the cover cap and sealing member, a current control member disposed between the cover cap and the sealing member to reportedly cut-off a flow of current when a temperature of the battery is increased above an allowable level, and a shock absorber disposed between the cover cap and current control member to reportedly prevent shock from being directly transmitted to the current control member.
U.S. Pat. No. 6,777,128 relates to a secondary battery and a fabrication method of the secondary battery which includes a battery unit having a positive electrode plate, a negative electrode plate and a separator interposed therebetween, a can for accommodating the battery unit, a cap assembly having a cap cover, a safety vent and a gasket, where the end of the safety vent is bent inwards to be filled with the gasket provided along the outer periphery of the safety vent reportedly so that the safety vent is inserted into the gasket in a secure manner.
U.S. Publication No. 2005/0244706 relates to an electrochemical cell with a collector assembly for sealing the open end of a cell container. The collector assembly includes a retainer and a contact spring with a peripheral flange, each having a central opening therein. A pressure release vent member disposed between the retainer and the peripheral flange of the contact spring reportedly seals the openings in the retainer and contact spring under normal conditions and ruptures to release pressure from within the cell when the internal pressure exceeds a predetermined limit.
U.S. Publication No. 2006/0228620 relates to a closure assembly and rupturable vent seal adapted for use in an electrochemical battery cell. The vent seal includes a series of peripheral projections that can be folded to insure proper sealing of the vent without wrinkles or overlapping folded portions.
U.S. Publication No. 2007/0015046 relates to a lithium secondary battery having protrusions or depressions formed on a surface of a gasket which makes contact with a safety vent so that gas, which is generated inside the battery, and an electrolyte, reportedly do not leak, thereby reportedly improving safety of the battery.
U.S. Publication No. 2008/0070109 relates to a flat-shaped non-aqueous electrolyte secondary battery that includes an electrode body formed by opposing a positive electrode and a negative electrode while interposing a separator therebetween, an outer case for housing the electrode body, and a sealing plate for sealing an opening of the outer case and an end part of the sealing plate positioned inside the outer case. Also, the sealing plate functions as a positive electrode terminal, the outer case functions as a negative electrode terminal, and a surface layer of the sealing plate in contact with the positive electrode is formed with a metal layer made of aluminum or aluminum alloy.
Japanese Publication No. 09-274900 relates to a nonaqueous secondary battery with a structure that reportedly does not cause electrolyte leakage and reportedly provides an increase of battery resistance to impact applied.
Japanese Publication No. 10-340714 prevents breakage of an explosion proof valve body and reportedly develops this function by arranging the explosion proof valve body on the inside of a battery more than a terminal cap and connecting an electrode lead to the explosion-proof valve body through a welding plate.
Japanese Publication No. 2007-141673 provides a bobbin-type lithium primary battery whose cost can be reduced by using a nickel-plated steel plate as the material for a positive electrode can that can be reportedly used and preserved for a long period.
In view of the disclosures above, it would be desirable to provide an electrochemical cell having a closure assembly having an end assembly that exhibits desirable barrier properties to vapor transmission while still allowing emergency venting as necessary via a vent member.